Search

Aim: Species interactions are predicted to become stronger toward low latitudes and elevations, and these predictions have been supported in large experiments measuring daily predation rates on early life‐stages. However, the overall strength and importance of predation depend on both the daily risk of being attacked and how long prey are exposed, and gradients in exposure time are rarely quantified. Here, we test whether time‐to‐germination, which determines seeds' exposure to post‐dispersal attack, is faster in high‐predation environments: low latitudes, low elevations, and warmer wetter climates. Location: Global data synthesis. Taxon: Angiosperms. Methods: We synthesized data on time‐to‐germination from 1410 plant species spanning 118° latitude. We divided data by study environment (lab, greenhouse, garden, nature), as we predicted different patterns depending on whether seeds experienced only intrinsic versus intrinsic + extrinsic germination cues. We tested how mean days‐to‐germination varied with geography (latitude, elevation) and climate (annual mean and seasonality of temperature and precipitation). We also explored whether patterns could be explained by seed size or phylogeny, which vary latitudinally. Results: Seeds germinated faster toward higher latitudes across study environments but slower toward higher elevations when experiencing intrinsic + extrinsic germination cues (in nature). Germination was faster in drier, more seasonal and—when tested in nature—warmer environments. Seed size explained some latitudinal variation in time‐to‐germination, whereas accounting for phylogeny did not improve predictions. Germination was slower in natural versus lab environments. Main Conclusions: We found little evidence that seeds have commonly evolved faster germination in high‐predation environments. While time‐to‐germination varied with geography and climate, patterns were inconsistent among predictors, and were weaker than those reported for daily seed predation rates. Detected gradients in time‐to‐germination would partially counter elevational gradients in daily seed predation rates but exacerbate latitudinal gradients in predation rates, such that tropical seeds likely experience much stronger lifetime predation risk than high‐latitude seeds. [ABSTRACT FROM AUTHOR]

Aim: Altitudinal and latitudinal treeline ecotones have not consistently responded to climate warming in the direction and/or magnitude predicted by climate alone, suggesting that non‐climatic mechanisms (e.g. biotic interactions) also mediate treeline range dynamics. Through a collaborative research approach, we assessed environmental conditions associated with pre‐dispersal insect cone granivory and how this biotic interaction may govern the reproductive potential, and therefore range dynamics, of spruce‐dominated treelines across northern Canada. Location: In all, 10 boreal forest treelines, tundra and alpine, from Yukon to Newfoundland and Labrador, Canada. Taxa: White spruce (Picea glauca [Moench] Voss), Black spruce (Picea mariana [Mill.] B.S.P.), Strobilomyia spp., Megastigmus spp. Methods: Treeline sites were assessed for presence and magnitude of pre‐dispersal seed granivory by insects along with viable seed availability. We quantified stand density metrics, organic layer depth and understorey vegetation composition at each location and, subsequently, incorporated those variables into generalized linear mixed models to establish predictors of granivory magnitude and viability of available seed. Results: Insect granivory was widespread across sites; however, site‐specific patterns of granivory were associated with increased moss cover and decreased shrub cover and stand density. While all black spruce‐dominated sites exhibited seed viability rates > 50%, the number of seeds produced per cone varied, suggesting that within‐site abiotic conditions and biotic interaction pressures limit successful colonization of novel environments in advance of seed dispersal. Main Conclusions: The modelled relationships between granivory, seed viability and environmental conditions represent an essential step towards generalizing how and when biotic interactions across subarctic treelines influence boreal tree range dynamics before seed dispersal. Connections between granivory magnitude and site‐level treeline characteristics (e.g. stand density, understorey vegetation) will provide a more comprehensive understanding of treeline range dynamics under continued climate change. [ABSTRACT FROM AUTHOR]

Aim: Abundances of animals vary according to species‐specific habitat selection, but habitats are undergoing rapid change in response to anthropogenic alterations of land use and climate. The long‐term decline of snowfall is one of the most dramatic abiotic changes in boreal regions, with potential to alter species communities and shape future ecosystems. However, the effects of snow cover on habitat‐specific abundances remain unclear for many taxa. Here we explore whether long‐term declines in snow cover affect the abundances of overwintering birds. Taxon Fifty bird species. Location: Finland, Northern Europe. Methods: We used generalized linear mixed models to analyse citizen‐led monitoring data from 196 transects over a 32‐year period to assess whether abundances of birds have changed in built‐up areas, farmlands and forests, and whether these covary with warming temperatures and decreasing snow. We then explored if changes in abundance can be explained by body mass, migration strategy or feeding guilds of the species. Results: Over the study period, the abundance of overwintering birds increased. This increase was most pronounced in farmlands (69.6%), where abundances were positively associated with decreasing snow depth. On the other hand, while abundances in built‐up habitats (19.5%) decreased over the study period, they increased in periods of high snow depths. Finally, we found that the short‐distance migration strategy explains changes in bird abundances with snow. In farmlands, ground feeding birds and heavier birds also show a positive trends in abundance with decreasing snow depths. Main conclusions: Local snow conditions are driving habitat selection of birds in the winter; birds in farmlands were most responsive to a decrease in snow depth. Changing snow depths can affect bird movements across habitats in the winter, but also influence migratory patterns and range shifts of species. [ABSTRACT FROM AUTHOR]